LibWeb: Stop leaking entire realms via Blob URLs

This patch implements the File API spec's supplemental steps for
document's "unloading document cleanup steps" so that we now remove blob
URLs associated with the document's relevant settings object when the
document is being unloaded.

Fixes two realm leaks when running our test suite.

Userland/Libraries/LibWeb/DOM/Document.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2023, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2018-2024, Andreas Kling <kling@serenityos.org>
  * Copyright (c) 2021-2023, Linus Groh <linusg@serenityos.org>
  * Copyright (c) 2021-2023, Luke Wilde <lukew@serenityos.org>
  * Copyright (c) 2021-2023, Sam Atkins <atkinssj@serenityos.org>
@@ -52,6 +52,7 @@
 #include <LibWeb/DOM/Text.h>
 #include <LibWeb/DOM/TreeWalker.h>
 #include <LibWeb/Dump.h>
+#include <LibWeb/FileAPI/BlobURLStore.h>
 #include <LibWeb/HTML/AttributeNames.h>
 #include <LibWeb/HTML/BrowsingContext.h>
 #include <LibWeb/HTML/CustomElements/CustomElementDefinition.h>
@@ -2988,6 +2989,8 @@ void Document::run_unloading_cleanup_steps()
         // 2. Clear window's map of active timers.
         window->clear_map_of_active_timers();
     }
+
+    FileAPI::run_unloading_cleanup_steps(*this);
 }
 
 // https://html.spec.whatwg.org/multipage/document-lifecycle.html#destroy-a-document

Userland/Libraries/LibWeb/FileAPI/BlobURLStore.cpp

@@ -1,12 +1,14 @@
 /*
  * Copyright (c) 2023, Tim Flynn <trflynn89@serenityos.org>
+ * Copyright (c) 2024, Andreas Kling <kling@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
 #include <AK/StringBuilder.h>
 #include <LibURL/URL.h>
 #include <LibWeb/Crypto/Crypto.h>
+#include <LibWeb/DOM/Document.h>
 #include <LibWeb/FileAPI/Blob.h>
 #include <LibWeb/FileAPI/BlobURLStore.h>
 #include <LibWeb/HTML/Origin.h>
@@ -89,4 +91,19 @@ ErrorOr<void> remove_entry_from_blob_url_store(StringView url)
     return {};
 }
 
+// https://w3c.github.io/FileAPI/#lifeTime
+void run_unloading_cleanup_steps(JS::NonnullGCPtr<DOM::Document> document)
+{
+    // 1.  Let environment be the Document's relevant settings object.
+    auto& environment = document->relevant_settings_object();
+
+    // 2.  Let store be the user agent’s blob URL store;
+    auto& store = FileAPI::blob_url_store();
+
+    // 3. Remove from store any entries for which the value's environment is equal to environment.
+    store.remove_all_matching([&](auto&, auto& value) {
+        return value.environment == &environment;
+    });
+}
+
 }

Userland/Libraries/LibWeb/FileAPI/BlobURLStore.h

@@ -28,4 +28,6 @@ ErrorOr<String> generate_new_blob_url();
 ErrorOr<String> add_entry_to_blob_url_store(JS::NonnullGCPtr<Blob> object);
 ErrorOr<void> remove_entry_from_blob_url_store(StringView url);
 
+void run_unloading_cleanup_steps(JS::NonnullGCPtr<DOM::Document>);
+
 }